Lithium ion battery

Abstract

In order to solve the problems that an existing high-voltage lithium ion battery is insufficient in positive electrode stability and electrolyte is decomposed to produce gas, the invention provides a lithium ion battery which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the surface of the positive electrode active material is provided with a lithium phosphate coating layer, and the non-aqueous electrolyte is coated on the surface of the negative electrode material layer. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises cyclic carbonate containing fluoroethylene carbonate, and the additive comprises a compound as shown in a structural formula 1 and a compound as shown in a structural formula 2; the lithium ion battery satisfies the following conditions: 0.2 < = P * (A + B) / (100-C) < = 2.25, 30 < = P < = 150, 10 < = C < = 20, 0.05 < = A < = 0.5, and 0.3 < = B < = 1. The lithium ion battery provided by the invention can keep the intrinsic material stability of the positive electrode active material under a high working voltage condition, and meanwhile, the gas production of the lithium ion battery at a high temperature is obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of energy storage components, and in particular relates to a lithium ion battery. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, wide operating temperature range, high energy density, high output power, no memory effect and long cycle life. They are not only widely used in 3C digital products such as mobile phones and laptops, but also have a broad application market in new energy vehicles and large-scale energy storage. With the rapid development of new energy, the application of non-aqueous electrolyte lithium-ion batteries has also grown by leaps and bounds. However, with the urgent demand of end users to improve the range of new energy vehicles, it is necessary to further improve the energy density of power batteries.

[0003] Compared with the commonly used battery systems (lithium iron phosphate system, ternary system) on the market, the spinel structure of lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) and lithium-rich materials have higher energy density and power density. At the same time, because they do not contain cobalt, they have the advantage of low cost and are suitable for power batteries and large-scale energy storage applications. They are the two most promising and attractive positive electrode materials in the future development of lithium-ion batteries. Among them, spinel structured lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) has a three-dimensional diffusion channel, and its theoretical discharge capacity can reach 147 mAh g -1 , the voltage platform is as high as 4.7V; while the lithium-rich material has a higher specific capacity (≥250mAh / g), and its application voltage is also higher than 4.5V.

[0004] In actual application, it is found that under high-voltage system, the intrinsic stability of the material is reduced, and the lattice destruction and ion dissolution cause performance degradation; at the same time, the electrolyte is prone to decomposition under high potential, and gas production and interface film loss further aggravate performance degradation. The performance degradation of the electrolyte under high voltage can be suppressed to a certain extent through positive electrode coating and oxidation-resistant electrolyte design, but under high temperature conditions, gas production and capacity loss are "hard injuries" that are difficult to solve. In order to meet the performance requirements of electric vehicles for batteries, it is necessary to provide a targeted electrolyte with good high-temperature performance and a high-voltage lithium-ion battery. Summary of the invention

[0005] In view of the problems of insufficient positive electrode stability and gas generation due to electrolyte decomposition in existing high-voltage lithium-ion batteries, the present invention provides a lithium-ion battery.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows: The present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the surface of the positive electrode active material has a lithium phosphate coating layer, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises a cyclic carbonate containing fluoroethylene carbonate, and the additive comprises a compound represented by structural formula 1 and a compound represented by structural formula 2; Structural formula 1 Wherein, R1, R2, and R3 are each independently selected from a C1-C5 alkyl or halogenated alkyl, a C2-C5 unsaturated hydrocarbon group or an unsaturated halogenated hydrocarbon group, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or the unsaturated halogenated hydrocarbon group; Structural formula 2 Wherein, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group; The lithium-ion battery meets the following conditions: 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1; Wherein, P is the thickness of the lithium phosphate coating layer, in nm; C is the mass percentage of cyclic carbonate in the non-aqueous electrolyte, unit is % A is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in units of %; B is the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte, in %.

[0007] Optionally, the lithium-ion battery meets the following conditions: 0.32≤P×(A+B) / (100-C)≤1.2, and / or The thickness P of the lithium phosphate coating layer is 50-100 nm, and / or The mass percentage C of the cyclic carbonate in the non-aqueous electrolyte is 12% to 17%, and / or The mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.05% to 0.3%, and / or The mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.5% to 0.8%.

[0008] Optionally, the cyclic carbonate further includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate.

[0009] Optionally, in Structural Formula 1, the C1-C5 alkyl group is selected from methyl, ethyl, propyl, isopropyl or butyl; the C1-C5 haloalkyl group is selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl or hexafluoroisopropyl; the C2-C5 unsaturated hydrocarbon group is selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl or 1-methyl-2-propynyl; Preferably, the compound shown in the structural formula 1 includes one or more of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0010] Optionally, in structural formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a fluorine atom or a C1-C5 group, and the C1-C5 group includes one or more of a trifluoromethyl group, a C1-C5 hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, and a cyano-substituted hydrocarbon group.

[0011] Optionally, the compound represented by structural formula 2 includes one or more of the following compounds:

[0012] Optionally, the mass percentage F% of fluoroethylene carbonate in the non-aqueous electrolyte satisfies: 0.3≤F≤4.

[0013] Optionally, the non-aqueous electrolyte satisfies the following condition: 0.05≤(F+B) / C≤0.5.

[0014] Optionally, the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, an unsaturated cyclic carbonate compound, a silane phosphate compound and a nitrile compound; The cyclic sulfate ester compound includes at least one of propylene sulfate and methyl vinyl sulfate; and / or The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone; and / or The unsaturated cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinyl carbonate, and ethylene methylene carbonate: and / or The silane phosphate compounds include at least one of tris(trimethylsilyl) phosphate and tris(triethylsilyl) phosphate: and / or The nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0015] Optionally, the non-aqueous organic solvent further includes one or more of chain carbonates, carboxylic ester solvents, and ether solvents.

[0016] Optionally, the positive electrode active material includes at least one of the compounds represented by formula (A) or formula (B): LiNi x M 2-x A y O r B p Formula (A) nLi2MnO3·(1-n)LiMO2, formula (B) In formula (A), 0≤x≤1, 0≤2-x≤2, 0≤y≤0.05, 1≤r≤4, 0≤p≤4, r + p≤4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br; In formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn, or Al. According to the lithium ion battery provided by the present invention, a cyclic carbonate containing fluoroethylene carbonate, a compound shown in structural formula 1 and a compound shown in structural formula 2 are added to a non-aqueous electrolyte, and a lithium phosphate coating layer is coated on the surface of the positive electrode active material. The lithium phosphate coating layer has a certain protective effect on the positive electrode active material to inhibit the dissolution of transition metals (such as Mn) in the positive electrode active material. In the battery formation stage, the cyclic carbonate, the compound shown in structural formula 1 and the compound shown in structural formula 2 are decomposed on the positive electrode surface and participate in the formation of the positive electrode surface interface film. The positive electrode surface interface film has a good barrier protection effect on the non-aqueous electrolyte. Used to reduce the decomposition and gas generation of the non-aqueous electrolyte under high voltage, the lithium phosphate coating layer and the positive electrode surface interface film are mutually embedded on the surface of the positive electrode active material to form an organic-inorganic protective layer; the inventors have found through a large number of studies that when the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte and the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte meet the conditions of 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0 .5, 0.3≤B≤1, the obtained lithium ion battery can maintain the intrinsic material stability of the positive electrode active material under high working voltage conditions, and the gas production of the lithium ion battery at high temperature is significantly reduced. It is speculated that the cyclic carbonate, the compound shown in structural formula 1 and the compound shown in structural formula 2 have a competitive relationship in forming the positive electrode surface interface film. By adjusting the content of the three, the composition of the positive electrode surface interface film can be regulated, thereby obtaining a positive electrode surface interface film with higher bonding strength with the lithium phosphate coating layer. At the same time, the thickness of the lithium phosphate coating layer affects the formation density of the positive electrode surface interface film. Generally, the lithium phosphate coating layer The higher the thickness, the lower the thickness of the positive electrode surface interface film formed, which in turn affects the isolation and protection effect of the organic-inorganic protective layer on the positive electrode and the non-aqueous electrolyte. When the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte and the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte are under synergistic conditions, the obtained organic-inorganic protective layer is stable under high voltage, which can effectively improve the stability of the positive electrode active material and the non-aqueous electrolyte under high operating voltage, and improve the electrochemical performance of high-voltage lithium-ion batteries. DETAILED DESCRIPTION

[0017] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] An embodiment of the present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the surface of the positive electrode active material has a lithium phosphate coating layer, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises a cyclic carbonate containing fluoroethylene carbonate, and the additive comprises a compound shown in Structural Formula 1 and a compound shown in Structural Formula 2; Structural formula 1 Wherein, R1, R2, and R3 are each independently selected from a C1-C5 alkyl or halogenated alkyl, a C2-C5 unsaturated hydrocarbon group or an unsaturated halogenated hydrocarbon group, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or the unsaturated halogenated hydrocarbon group; Structural formula 2 Wherein, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group; The lithium-ion battery meets the following conditions: 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1; Wherein, P is the thickness of the lithium phosphate coating layer, in nm; C is the mass percentage of cyclic carbonate in the non-aqueous electrolyte, unit is % A is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in units of %; B is the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte, in %.

[0019] The lithium phosphate coating layer has a certain protective effect on the positive electrode active material to inhibit the dissolution of transition metals (such as Mn) in the positive electrode active material. In the battery formation stage, the cyclic carbonate, the compound shown in structural formula 1 and the compound shown in structural formula 2 decompose on the positive electrode surface and participate in the formation of the positive electrode surface interface film. The positive electrode surface interface film has a good barrier protection effect on the non-aqueous electrolyte, reducing the decomposition and gas production of the non-aqueous electrolyte under high voltage. The lithium phosphate coating layer and the positive electrode surface interface film are interlocked with each other on the surface of the positive electrode active material to form an organic-inorganic protective layer; the inventors have found through a lot of research that when the thickness P of the lithium phosphate coating layer, the cyclic carbonate in the non-aqueous electrolyte, and the organic-inorganic protective layer on the positive electrode surface are the same, the lithium phosphate coating layer and the positive electrode surface interface film are the same. When the mass percentage content C of the ester, the mass percentage content A of the compound represented by the structural formula 1 in the non-aqueous electrolyte, and the mass percentage content B of the compound represented by the structural formula 2 in the non-aqueous electrolyte satisfy the conditions of 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, and 0.3≤B≤1, the obtained lithium ion battery can maintain the intrinsic material stability of the positive electrode active material under high operating voltage conditions, and the gas generation of the lithium ion battery at high temperature is significantly reduced. Less, it is speculated that the cyclic carbonate, the compound shown in structural formula 1 and the compound shown in structural formula 2 have a competitive relationship when forming the positive electrode surface interface film. By adjusting the content of the three, the composition of the positive electrode surface interface film can be regulated, thereby obtaining a positive electrode surface interface film with higher bonding strength with the lithium phosphate coating layer. At the same time, the thickness of the lithium phosphate coating layer affects the formation density of the positive electrode surface interface film. Generally, the higher the thickness of the lithium phosphate coating layer, the lower the thickness of the positive electrode surface interface film formed, thereby affecting the isolation and protection effect of the organic-inorganic protective layer on the positive electrode and the non-aqueous electrolyte. When the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte and the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte are under synergistic conditions, the obtained organic-inorganic protective layer is stable under high voltage, which can effectively improve the stability of the positive electrode active material and the non-aqueous electrolyte under high working voltage, and improve the electrochemical performance of high-voltage lithium-ion batteries.

[0020] In a preferred embodiment, the lithium-ion battery meets the following conditions: 0.32≤P×(A+B) / (100-C)≤1.2.

[0021] When the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte and the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte further meet the above conditions, it is beneficial to further inhibit the dissolution of transition metal ions of the positive electrode active material under high voltage, and at the same time inhibit the decomposition and gas production of the non-aqueous electrolyte at high temperature.

[0022] In a specific embodiment, the thickness P of the lithium phosphate coating layer can be 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm or a range between any two of the above values.

[0023] In a preferred embodiment, the thickness P of the lithium phosphate coating layer is 50-100 nm.

[0024] By setting a lithium phosphate coating layer of reasonable thickness on the surface of the positive electrode active material, the corrosion effect of the non-aqueous electrolyte on the surface of the positive electrode active material can be reduced, so that the positive electrode-electrolyte interface can be maintained stable under high voltage, and the crystal structure can be prevented from collapsing, so that it has better cycle performance. However, the thickness of the coating layer has an impact on the specific capacity of the material. The thicker the coating, the lower the specific capacity of the material, resulting in low capacity. It will also affect the formation of the interface film on the positive electrode surface. The design of non-aqueous electrolyte under high pressure conditions needs to consider the decomposition and gas production caused by the contact between the positive electrode active material and the non-aqueous electrolyte. The positive electrode coating layer blocks the contact between the non-aqueous electrolyte and the material body to a certain extent. The thicker the lithium phosphate coating layer, the lower the demand for additives for the non-aqueous electrolyte to form the positive electrode surface interface film during the formation stage. Within the above lithium phosphate coating thickness range, it is beneficial to protect the positive electrode activity without causing significant capacity loss, and it is beneficial to ensure the synergy with the positive electrode surface interface film.

[0025] The thickness of the lithium phosphate coating on the surface of the positive electrode active material can be detected by XPS etching or TEM. The test method is: the battery is discharged to 0% SOC, and after disassembly, the positive electrode plate is cleaned with DMC, and then the plate is ion milled (CP) or FIB cut. The P element distribution based on SEM-mapping can be used to preliminarily confirm the thickness of the coating. In some embodiments, in order to achieve more accurate thickness detection, electron probe microanalysis (EPMA) can be used to perform line scanning or surface scanning analysis on a single particle, and the thickness of the lithium phosphate coating can be confirmed in combination with the element distribution curve.

[0026] In a specific embodiment, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range between any two of the above values.

[0027] In a preferred embodiment, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte is 12% to 17%.

[0028] Cyclic carbonates have excellent film-forming properties. If the mass percentage C of the cyclic carbonate is too small, it is difficult to form a positive electrode surface interface film with good stability on the surface of the positive electrode active material; if the mass percentage C of the cyclic carbonate is too large, it will cause the viscosity of the non-aqueous electrolyte to increase, affecting the wetting of the non-aqueous electrolyte to the positive electrode material layer and the ion conduction efficiency. In addition, under high voltage conditions (≥4.5V), especially in high temperature environments, the decomposition of the cyclic carbonate is aggravated, and it is easy to combine with electrons to decompose and produce carbon gases (CO, CO2, alkanes / olefins), and it is easy to be catalyzed by transition metal ions to produce solvated hydrogen structures, inducing the production of hydrogen, resulting in increased gas production in the electrolyte.

[0029] In a specific embodiment, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5% or a range between any two of the above values.

[0030] In a preferred embodiment, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.05% to 0.3%.

[0031] The compound shown in structural formula 1 tends to form a film on the positive electrode surface during the battery formation stage, and the phosphorus-containing component in its decomposition product has good affinity with the lithium phosphate coating layer, which can improve the bonding strength between the positive electrode surface interface film and the lithium phosphate coating layer. If the addition amount of the compound shown in structural formula 1 is too low, the bonding strength between the positive electrode surface interface film and the lithium phosphate coating layer is affected; if the addition amount of the compound shown in structural formula 1 is too high, the content of the components derived from the compound shown in structural formula 2 and the cyclic carbonate in the positive electrode surface interface film is affected, which has an adverse effect on the film formation quality of the positive electrode surface interface film.

[0032] In a specific embodiment, the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte can be 0.3%, 0.4%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1% or the range between any two of the above values.

[0033] In a preferred embodiment, the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.5% to 0.8%.

[0034] The compound shown in Structural Formula 2 participates in the formation of the positive electrode surface interface film and the negative electrode surface interface film at the same time, effectively improving the thermal stability of the positive electrode surface interface film and the negative electrode surface interface film, and inhibiting the generation of hydrogen caused by the migration of solvated hydrogen. If the addition amount of the compound shown in Structural Formula 2 is too low, it will affect the thermal stability of the positive electrode surface interface film and the negative electrode surface interface film; if the addition amount of the compound shown in Structural Formula 2 is too high, it will affect the synergistic effect with the compound shown in Structural Formula 1 and the cyclic carbonate, which is also not conducive to improving the film quality.

[0035] In some embodiments, the cyclic carbonate further includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0036] In some embodiments, in Structural Formula 1, the C1-C5 alkyl group is selected from methyl, ethyl, propyl, isopropyl or butyl; the C1-C5 haloalkyl group is selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl or hexafluoroisopropyl; the C2-C5 unsaturated hydrocarbon group is selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl or 1-methyl-2-propynyl.

[0037] In a preferred embodiment, the compound shown in structural formula 1 includes one or more of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0038] In some embodiments, in structural formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a fluorine atom, or a C1-C5 group, and the C1-C5 group includes one or more of a trifluoromethyl group, a C1-C5 hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, and a cyano-substituted hydrocarbon group.

[0039] In a preferred embodiment, the compound represented by structural formula 2 includes one or more of the following compounds:

[0040] In some embodiments, the mass percentage F% of fluoroethylene carbonate in the non-aqueous electrolyte satisfies: 0.3≤F≤4.

[0041] In some embodiments, the non-aqueous electrolyte satisfies the following condition: 0.05≤(F+B) / C≤0.5.

[0042] In this embodiment, fluoroethylene carbonate is not used as the main solvent, but only as an auxiliary solvent to enhance the intrinsic pressure resistance of the electrolyte, which can take into account both system stability and gas production inhibition. After extensive research, the inventors found that when a lithium phosphate coating is provided on the surface of the high-voltage positive electrode material crystal, and the cyclic carbonate contains a certain amount of fluoroethylene carbonate, the amount of non-fluorinated carbonate in the electrolyte can be reduced to 20% or less, and as the positive electrode lithium phosphate coating thickens, the content of non-fluorinated carbonate can be further reduced. It is speculated that this is because: the lithium phosphate coating enhances the structural stability of the positive electrode active material, ion dissolution and lattice fragmentation are inhibited, and the catalytic effect of the electrolyte is weakened; at the same time, the fluorine atoms of fluoroethylene carbonate in the cyclic carbonate have strong electronegativity and weak polarity, which can effectively increase the oxidation decomposition voltage of the solvent, and it is easy to obtain a solvent that meets the requirements for the use of high-voltage electrolytes. However, fluoroethylene carbonate induces more gas production than other non-fluorinated carbonates (such as EC) under high voltage. This is related to the generation of free radicals by the breaking of the carbon-oxygen bond of the linear ester under high pressure: EC is easier to decompose, and the decomposition of the linear ester is incomplete at this time. The solvated hydrogen produced by the decomposition of the non-fluorinated carbonate migrates more to the negative electrode to react, while the fluoroethylene carbonate decomposes later, and the free radicals produced by the linear ester combine with the solvated hydrogen to generate more carbon gases (such as CO, CO2 or alkanes / olefins). At the same time, the compound shown in Structural Formula 2 has similar chemical properties to non-fluorinated carbonates. Therefore, by controlling the cyclic carbonate, fluoroethylene carbonate and the compound shown in Structural Formula 2 to meet the conditions of 0.05≤(F+B) / C≤0.5, and 10≤C≤20, 0.3≤F≤4, 0.3≤B≤1, it is beneficial to synergize the effects of the three on the stability of the non-aqueous electrolyte and reduce the gas production of lithium-ion batteries at high temperatures.

[0043] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions: 0.06≤(F+B) / C≤0.3; preferably 12≤C≤17, 0.5≤F≤3, 0.5≤B≤0.8.

[0044] In some embodiments, the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, an unsaturated cyclic carbonate compound, a silane phosphate compound, and a nitrile compound.

[0045] In some embodiments, the cyclic sulfate ester compound includes at least one of propylene sulfate and methyl vinyl sulfate.

[0046] In some embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

[0047] In some embodiments, the unsaturated cyclic carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, and methylene vinyl carbonate.

[0048] In some embodiments, the silane phosphate compound includes at least one of tris(trimethylsilane) phosphate and tris(triethylsilane) phosphate.

[0049] In some embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile.

[0050] In some embodiments, the lithium salt includes LiPF6, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, a lower aliphatic lithium carboxylate having 4 or less carbon atoms, or at least one of lithium tetraphenylborate.

[0051] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5mol / L, 0.55mol / L, 0.6mol / L, 0.65mol / L, 0.7mol / L, 0.8mol / L, 0.85mol / L, 0.9mol / L, 0.95mol / L, 1.0mol / L, 1.1mol / L, 1.15mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.45mol / L, 1.5mol / L, 1.6mol / L, 1.7mol / L, 1.8mol / L, 1.9mol / L, 2.0mol / L, 2.1mol / L, 2.2mol / L, 2.3mol / L, 2.4mol / L or 2.5mol / L.

[0052] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent is 65% to 90%.

[0053] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, or 90%.

[0054] In some embodiments, the non-aqueous organic solvent further comprises one or more of linear carbonates, carboxylic acid ester solvents and ether solvents.

[0055] In some embodiments, the chain carbonate may be specifically but not limited to at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within the range of not significantly damaging the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the large current discharge characteristics of the non-aqueous electrolyte battery, the stability relative to the negative electrode, and the cycle characteristics reach a good range. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby helping to improve the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolytic solution, is usually more than 15% by volume, preferably more than 20% by volume, more preferably more than 25% by volume. In addition, usually below 90% by volume, preferably below 85% by volume, more preferably below 80% by volume. By making the content of linear carbonate in above-mentioned scope, easily make the viscosity of nonaqueous electrolytic solution reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to make the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate satisfy above-mentioned scope.

[0056] In certain embodiments, it is also possible to preferably use chain carbonates with fluorine atoms (hereinafter referred to as "fluorinated chain carbonates"). The number of fluorine atoms possessed by the fluorinated chain carbonate is not particularly limited as long as it is more than 1, but is generally less than 6, preferably less than 4. When the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded to the same carbon or to different carbons. As the fluorinated chain carbonate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc. can be listed.

[0057] In some embodiments, the carboxylate solvent includes cyclic carboxylate and / or chain carbonate. Examples of cyclic carboxylate include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonate include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0058] In some embodiments, the ether solvent includes cyclic ether or chain ether, preferably chain ether with 3 to 10 carbon atoms and cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether may be, but not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ionic conductivity, are particularly preferred. The ether compound can be used alone or in any combination and ratio. The amount of the ether compound added is not particularly limited, and is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. The volume ratio of the non-aqueous solvent is usually 1% or more, preferably 2% or more, and more preferably 3% or more, and the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less.

[0059] In some embodiments, the positive electrode active material includes at least one of the compounds represented by formula (A) or formula (B): LiNi x M 2-x A y O r B p Formula (A) nLi2MnO3·(1 - n)LiMO2 of formula (B) In formula (A), 0 ≤ x ≤ 1, 0 ≤ 2 - x ≤ 2, 0 ≤ y ≤ 0.05, 1 ≤ r ≤ 4, 0 ≤ p ≤ 4, r + p ≤ 4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br; In formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn or Al. In some specific embodiments of the present invention, when the positive electrode active material of the lithium - ion battery of the present invention includes the compound represented by formula (A), the positive electrode active material includes LiNi 0.5 Mn 1.5 O4.

[0060] In some specific embodiments of the present invention, when the positive electrode active material of the lithium - ion battery of the present invention includes the compound represented by formula (B), the positive electrode active material may include 0.1Li2MnO3·0.9LiNi 0.5 Mn 0.5 O2, 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2, 0.5Li2MnO3·0.5LiNi 0.4 Mn 0.6 O2, 0.6Li2MnO3·0.4LiNi 0.5 Mn 0.5 O2, 0.7Li2MnO3·0.3LiNi 0.5 Mn 0.5 O2, 0.8Li2MnO3·0.2LiNi 0.4 Mn 0.6 O2, 0.9Li2MnO3·0.1LiNi 0.4 Mn 0.6 O2, 0.7Li2MnO3·0.3LiNi 0.5 Con 0.2 Mn 0.3 O2 or at least one of them.

[0061] When the positive electrode active material of the lithium - ion battery is selected from the above - mentioned materials, the lithium - ion battery has a higher energy density and power density, and at the same time, due to the absence of cobalt, it has the advantage of low cost.

[0062] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, and the positive electrode active material, the positive electrode binder and the positive electrode conductor are blended to obtain the positive electrode material layer.

[0063] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0064] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0065] In some embodiments, the positive electrode current collector includes a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0066] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin carbon, tin oxygen, and tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.

[0067] In a more preferred embodiment, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, graphene, and silicon-carbon composite materials.

[0068] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0069] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector comprises a metal material that can conduct electrons, preferably, the negative electrode current collector comprises at least one of Al, Ni, tin, copper, and stainless steel, and in a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0070] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0071] The negative electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0072] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0073] In some embodiments, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0074] The diaphragm may be an existing conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, an inorganic-organic composite diaphragm, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP diaphragms.

[0075] The present invention is further described below by way of examples.

[0076] Table 1 Example 1 This embodiment is used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and includes the following steps: The positive electrode preparation steps are as follows: a lithium nickel manganese oxide active material LNMO with a lithium phosphate coating layer, conductive carbon black and a binder polyvinylidene fluoride are mixed in a mass ratio of 94.5:3.0:2.5, dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, and the positive electrode slurry is evenly coated on both sides of an aluminum foil, and then dried, rolled and vacuum dried, and an aluminum lead wire is welded with an ultrasonic welder to obtain a positive electrode plate. The thickness of the plate is between 120 and 150 μm, and the compaction density of the positive electrode material is controlled to be 3.1 g / cm by the surface density and rolling thickness of the positive electrode material. 3 , the thickness of the lithium phosphate coating is shown in Table 1.

[0077] The negative electrode preparation steps are as follows: graphite material, conductive carbon black, binder styrene butadiene rubber and carboxymethyl cellulose are mixed in a mass ratio of 95.2:1.0:2.4:1.4, dispersed in deionized water to obtain a negative electrode slurry, the negative electrode slurry is coated on both sides of the copper foil, and after drying, rolling and vacuum drying, a nickel lead wire is welded with an ultrasonic welder to obtain a negative electrode plate. The thickness of the plate is between 120-150 μm, and the compaction density of the negative electrode material is controlled to be 1.6 g / cm by the surface density and rolling thickness of the negative electrode material. 3 .

[0078] The electrolyte preparation steps are as follows: EC (ethylene carbonate), FEC (fluoroethylene carbonate), EMC (ethyl methyl carbonate), and DEC (diethyl carbonate) are mixed as non-aqueous solvents, wherein the addition amounts of EC (ethylene carbonate) and FEC (fluoroethylene carbonate) are as shown in Table 1, EMC and DEC are used to make up the solvent balance, and the mass ratio of EMC to DEC is 42:40; after mixing, LiPF6 with a concentration of 1 mol / L is added, and additives are added according to the weight percentage shown in Table 1.

[0079] The membrane preparation steps are as follows: using a three-layer isolation membrane of polypropylene, polyethylene and polypropylene with a thickness of 20 μm; The battery assembly steps are as follows: placing a three-layer isolation film with a thickness of 20 μm between the positive plate and the negative plate, then winding the sandwich structure consisting of the positive plate, the negative plate and the separator, flattening the wound body and placing it in an aluminum-plastic shell, welding the pole ears and sealing the aluminum-plastic shell to obtain a battery cell to be injected with liquid; cutting and injecting the electrolyte prepared above into the battery cell, sealing it after standing for 1 hour, and aging the sealed battery at 45°C for 48 hours.

[0080] Then the first charge formation was carried out according to the following steps: 0.05C constant current charging for 3h, 0.1C constant current charging for 2h, 0.2C constant current charging for 2h, standing for 1hr, aging at 45℃ for 48h, and then further charged to 4.85V at 0.2C constant current, and discharged to 3.4V at 0.2C constant current.

[0081] Embodiments 2 to 26 Examples 2 to 26 are used to illustrate the preparation method of the lithium ion battery disclosed in the present invention, and include most of the operation steps in Example 1, except that: The thickness of the lithium phosphate coating layer, the composition of the non-aqueous organic solvent, the additives and the amounts thereof are shown in Examples 2 to 26 in Table 1.

[0082] Comparative Examples 1 to 17 Comparative Examples 1 to 17 are used to illustrate the preparation method of the lithium ion battery disclosed in the present invention, and include most of the operation steps in Example 1, except that: The thickness of the lithium phosphate coating layer, the composition of the non-aqueous organic solvent, the additives and the amounts thereof are shown in Comparative Examples 1 to 17 in Table 1.

[0083] Performance Testing The lithium-ion battery prepared above was subjected to the following performance tests: The formed battery was charged to 4.85V at room temperature with 1C constant current and constant voltage, and then discharged to 3.4V with 1C constant current, and the initial discharge capacity was recorded. Then, it was charged to 4.85V with 1C constant current and constant voltage, and the initial volume of the battery was determined by the drainage method. Then, the battery was stored at 60℃ for 30 days. After the battery cooled to room temperature, the volume after storage was tested, and the battery retention capacity was measured by discharging to 3.4V with 1C. The calculation formula is as follows: First cycle discharge capacity (mAh / g) = initial discharge capacity / mass of active material × 100%; Battery capacity retention rate (%) = retention capacity / initial capacity × 100%; Battery volume expansion rate (%) = (volume after storage - initial volume) / initial volume × 100%; (1) The test results obtained in Examples 1 to 17 and Comparative Examples 1 to 17 are entered in Table 2.

[0084] Table 2 It can be seen from the test results of Examples 1 to 17 and Comparative Examples 1 to 17 that in a battery system using the compound represented by Structural Formula 1 and the compound represented by Structural Formula 2 as additives, a cyclic carbonate containing fluoroethylene carbonate as a non-aqueous organic solvent, and a lithium phosphate coating layer coated on the surface of the positive electrode active material, by controlling the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound represented by Structural Formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound represented by Structural Formula 2 in the non-aqueous electrolyte, so that the conditions of 0.2≤P×(A+B) / (100-C)≤2.25 are satisfied, and when 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, and 0.3≤B≤1, the obtained lithium ion battery has a higher capacity retention rate and a lower expansion rate under high temperature storage. It is speculated that the reason is that the cyclic carbonate, the compound shown in structural formula 1 and the compound shown in structural formula 2 compete with each other when constructing the positive electrode surface interface film. By adjusting the content ratio of these three components, the composition of the positive electrode surface interface film can be regulated, so as to obtain a positive electrode surface interface film that is more closely combined with the lithium phosphate coating layer. In addition, the thickness of the lithium phosphate coating layer affects the density of the positive electrode surface interface film, and then affects the effect of the organic-inorganic protective layer on the isolation and protection between the positive electrode and the non-aqueous electrolyte. When the thickness (P) of the lithium phosphate coating layer, the mass percentage content (C) of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage content (A) of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the mass percentage content (B) of the compound shown in structural formula 2 in the non-aqueous electrolyte are in a synergistic state, the organic-inorganic protective layer formed can remain stable under high voltage conditions. In this case, not only can the stability of the positive electrode active material and the non-aqueous electrolyte at high operating voltage be effectively improved, but also the electrochemical performance of high-voltage lithium-ion batteries can be significantly improved.

[0085] From the comparison of the test results of Examples 1 to 5 and Examples 6 to 17, it can be seen that when the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte further satisfy the conditions 0.32≤P×(A+B) / (100-C)≤1.2, and 50≤P≤100, 12≤C≤17, 0.05≤A≤0.3, 0.5≤B≤0.8, the adverse effect of the silicon-containing decomposition product of the second additive on the battery can be further suppressed, the battery impedance can be reduced, and the electrochemical performance stability of the battery at high temperature can be improved.

[0086] From the test results of comparative examples 1 to 10, it can be seen that when the P value, C value, A value, and B value do not meet their respective range limits, even if they meet the limit of 0.2≤P×(A+B) / (100-C)≤2.25, the obtained lithium ion battery does not have good high temperature storage performance, indicating that too high or too low P value, C value, A value, and B value are not conducive to the improvement of the high temperature performance of the lithium ion battery; from the test results of comparative examples 10 to 17, it can be seen that when the P value, C value, A value, and B value do not meet the limit of 0.2≤P×(A+B) / (100-C)≤2.25, even if they meet their respective content range limits, the high temperature performance of the lithium ion battery will also be deteriorated and the gas production will increase, indicating that there is a mutual influence between the compound shown in structural formula 1, the compound shown in structural formula 2, the cyclic carbonate with fluoroethylene carbonate, and the lithium phosphate coating layer, and only when and when the four reach a better equilibrium state can the performance of the battery be significantly improved.

[0087] (2) The test results obtained in Examples 1 to 4 and Examples 18 to 21 are entered in Table 3.

[0088] Table 3 From the comparison of the test results of Examples 1 to 4 and Examples 18 to 21, it can be seen that in the battery system provided by the present invention, when the non-aqueous electrolyte further satisfies the conditions 0.05≤(F+B) / C≤0.5, and 10≤C≤20, 0.3≤F≤4, 0.3≤B≤1, the high temperature storage performance and the first cycle discharge capacity of the battery can be further improved, wherein, under this condition, the lithium phosphate coating layer improves the structural stability of the positive electrode active material, inhibits ion dissolution and lattice fragmentation, and weakens the catalytic effect of the electrolyte. Fluorinated ethylene carbonate (FEC) in cyclic carbonates increases the oxidative decomposition voltage of the solvent due to the strong electronegativity and weak polarity of fluorine atoms, and is suitable for use in high-voltage electrolytes. However, at high voltage, FEC produces more gas than other non-fluorinated carbonates (such as EC), which is due to the fact that the linear ester breaks the carbon-oxygen bond under high pressure to generate free radicals: EC is easier to decompose, while FEC decomposes later, resulting in more carbon gases (such as CO, CO2 or alkanes / olefins) being generated. The compound shown in Structural Formula 2 has similar chemical properties to non-fluorinated carbonates and serves as a substitute for each other. Therefore, by controlling the ratio of cyclic carbonate, fluorinated ethylene carbonate and the compound shown in Structural Formula 2, the stability of the non-aqueous electrolyte can be synergistically enhanced and the gas generation of lithium-ion batteries at high temperatures can be reduced.

[0089] (3) The test results obtained in Examples 1 and 22 to 26 are entered in Table 4.

[0090] Table 4 It can be seen from the test results of Examples 1 and 22 to 26 that in the battery system of the present invention, under the premise of satisfying the conditions 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1, the use of different compounds represented by Structural Formula 1 and compounds represented by Structural Formula 2 has a good improvement effect on the high temperature storage performance and the first cycle discharge capacity in grams of lithium-ion batteries, indicating that the different compounds represented by Structural Formula 1 and the different compounds represented by Structural Formula 2 have commonalities in performance and produce similar effects in the electrolyte system.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer containing a positive electrode active material, the surface of the positive electrode active material has a lithium phosphate coating layer, the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, the non-aqueous organic solvent comprises a cyclic carbonate containing fluoroethylene carbonate, and the additive comprises a compound represented by structural formula 1 and a compound represented by structural formula 2; Structural formula 1 Wherein, R1, R2, and R3 are each independently selected from a C1-C5 alkyl or halogenated alkyl, a C2-C5 unsaturated hydrocarbon group or an unsaturated halogenated hydrocarbon group, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or the unsaturated halogenated hydrocarbon group; Structural formula 2 Wherein, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a halogen atom, or a C1-C5 group; The lithium-ion battery meets the following conditions: 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1; Wherein, P is the thickness of the lithium phosphate coating layer, in nm; C is the mass percentage of cyclic carbonate in the non-aqueous electrolyte, unit is % A is the mass percentage of the compound represented by structural formula 1 in the non-aqueous electrolyte, in units of %; B is the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte, in %.

2. The lithium-ion battery according to claim 1, characterized in that The lithium-ion battery meets the following conditions: 0.32≤P×(A+B) / (100-C)≤1.2, and / or The thickness P of the lithium phosphate coating layer is 50-100 nm, and / or The mass percentage C of the cyclic carbonate in the non-aqueous electrolyte is 12% to 17%, and / or The mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.05% to 0.3%, and / or The mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.5% to 0.8%.

3. The lithium-ion battery according to claim 1, characterized in that The cyclic carbonate further includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate.

4. The lithium-ion battery according to claim 1, characterized in that: In structural formula 1, the C1-C5 alkyl group is selected from methyl, ethyl, propyl, isopropyl or butyl; the C1-C5 haloalkyl group is selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl or hexafluoroisopropyl; the C2-C5 unsaturated hydrocarbon group is selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propargyl, 3-butynyl or 1-methyl-2-propynyl; Preferably, the compound represented by Structural Formula 1 includes one or more of triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate.

5. The lithium-ion battery according to claim 1, characterized in that: In Structural Formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a fluorine atom, or one of C1-C5 groups, and the C1-C5 groups include one or more of a trifluoromethyl group, a C1-C5 hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, and a cyano-substituted hydrocarbon group.

6. The lithium-ion battery according to claim 5, characterized in that: The compound represented by Structural Formula 2 includes one or more of the following compounds: 。 7. The lithium-ion battery according to claim 1, characterized in that: The mass percentage content F% of vinylene carbonate in the non-aqueous electrolyte satisfies: 0.3 ≤ F ≤ 4; Preferably, the non-aqueous electrolyte satisfies the following condition: 0.05 ≤ (F + B) / C ≤ 0.

5.

8. The lithium-ion battery according to claim 1, characterized in that The additive further includes at least one of cyclic sulfate compounds, sultone compounds, unsaturated cyclic carbonate compounds, silane phosphate compounds, and nitrile compounds; The cyclic sulfate compounds include at least one of propylene sulfate and vinyl methyl sulfate; and / or The sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; and / or The unsaturated cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, and methylene vinylene carbonate; and / or The silane phosphate compounds include at least one of tris(trimethylsilyl) phosphate and tris(triethylsilyl) phosphate; and / or The nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

9. The lithium-ion battery according to claim 1, characterized in that: The non-aqueous organic solvent further includes one or more of chain carbonates, carboxylic ester solvents, and ether solvents.

10. The lithium ion battery according to claim 1, characterized in that: The positive electrode active material includes at least one of the compounds represented by Formula (A) or Formula (B): LiNi x M 2-x A y O r B p Formula (A) nLi2MnO3·(1-n)LiMO2 Formula (B) In Formula (A), 0 ≤ x ≤ 1, 0 ≤ 2 - x ≤ 2, 0 ≤ y ≤ 0.05, 1 ≤ r ≤ 4, 0 ≤ p ≤ 4, r + p ≤ 4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br; In Formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn, or Al.

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